Theoretical study on the gas-phase ion-molecule SN2 and E2 reactions of halides of cycloalkanes

• Main Authors: Wan-Sam Lu, 呂宛珊
• Other Authors: Hu, Wei-Ping
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/e9496v

碩士 === 國立中正大學 === 化學暨生物化學研究所 === 103 === This thesis consists of three chapters. We studied the bimolecular nucleophilic substitution (SN2) and bimolecular elimination (E2) reactions of cyclic and noncyclic alkyl halides. In Chapter 1, we studied RX + SH( R=ethyl (C2H5), isopropyl (C3H7), tert-butyl (C4H9), cyclopentyl (C5H9), cyclohexyl (C6H11), n-propyl (C3H7), n-butyl (C4H9), n-pentyl (C5H11), n-hexyl (C6H13)；X=Cl、Br、I). For reactions of C4H9X (tert-butyl，X=Cl、Br、I) + SH and C5H9I (Iodocyclopentane) + SH, the elimination reactionas were favored . The substitution reactions were the most feasible pathway for the other reactions. When the reactant is cyclopentyl halide, the differences in barrier heights between substitution and elimination reactions ranged from 0.5 to 2.6 kcal/mol. The elimination reactions would compete with the substitution reactions. In chapter 2, we studied RX + CN( R=ethyl (C2H5), isopropyl (C3H7), tert-butyl (C4H9), cyclopentyl (C5H9), cyclohexyl (C6H11), n-propyl (C3H7) , n-butyl (C4H9), n-pentyl (C5H11), n-hexyl (C6H13)；X=Cl、Br、I) reactions. According to theoretical study of transition state theory (TST), the elimination reactions were favored over the substitution reactions for the C5H9X (cyclopentyl，X=Cl、Br、I) + CN. Especially, the rate constants of the elimination reactions were higher than theose of the substitution reactions by 1.6 to 15.6 times for the reactions of C5H9X (cyclopentyl，X=Cl、Br、I) + CN. The rate constants of the elimination reactions were higher than theose of the substitution reactions by 2.6 to 6 times for the reactions of C6H11X (cyclohexyl, X=Cl、Br、I) + CN. The substitution and the elimination pathways are competitive for the reactions of C5H9X and C6H11 X.l. In Chaper 3, we studied the identity exchange SN2 reactions of RX + X(R=ethyl (C2H5), isopropyl (C3H7), tert-butyl (C4H9), cyclopentyl (C5H9), cyclohexyl (C6H11), X=Cl、Br、I). The energy barrier of C5H9Cl + Cl(4.4kcal/mol) is lower than that of C3H7Cl + Cl(6.3 kcal/mol) by 1.9 kcal/mol. The deuterium KIEs of both cyclic and noncyclic halides were predicted to be normal with those of cyclic halides being slightly higher.